1. Field of the Invention
The present invention relates to gas separation membranes formed from certain substituted aromatic polyimides having a rigid polymer chain and to the process of separating one or more gases from a mixture of gases.
2. Prior Art
U.S. Pat. No. 4,705,540 discloses rigid polyimide gas separation membranes prepared from alkyl-substituted phenylene diamines and structurally rigid aromatic dianhydrides. Membranes prepared from these materials were found to have exceptionally high gas permeation rates with moderate gas selectivities.
U.S. Pat. No. 4,717,394 discloses that a greater range of gas productivities can be achieved through the controlled incorporation of less chain rigidity than that found in U.S. Pat. No. 4,705,540. This was accomplished, in part, through the use of mixtures of alkyl-substituted phenylene diamines and essentially unsubstituted diamines. The incorporation of alkyl-substituted methylene bisanilines with alkyl-substituted phenylene diamines in the present invention enables an even greater range of gas productivities to be achieved.
Application Ser. No. 175,503 filed Apr. 13, 1988 now U.S. Pat. No. 4,838,900 discloses polyimide gas separation membranes prepared from substituted methylene bisanilines and aromatic tetracarboxylic dianhydrides. The incorporation of the more rigid alkyl-substituted phenylene diamines in accordance with the present invention allows for a greater range of gas productivities than found in Ser. No. 175,503.
U.S. Pat. No. Re. 30,351; U.S. Pat. Nos. 3,822,202; and U.S. Pat. No. 3,899,309 disclose gas separation membrane materials comprising certain semi-rigid aromatic polyimides, polyamides and polyesters.